An investigation into the effects of New Zealand green-lipped mussel (Perna canaliculus) on non-haem iron absorption : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Human Nutrition at Massey University, Palmerston North, New Zealand

Abstract

The bioavailability of dietary non-haem iron can be influenced by the nutritional composition of a meal. Ascorbic acid and components within meat, fish and poultry, but particularly red meat and pork, all appear to enhance the absorption of non-haem iron when consumed together within a meal compared to other protein sources. However the promotion of red meat or pork is problematic due to their high saturated fatty acid content and alternative foods to red meat or pork that may enhance iron absorption such as oily fish or shellfish require further investigation. The aims of the present study were to investigate the effects of short-term and prolonged supplementation of New Zealand green-lipped mussel (Perna canaliculus) (NZGLM) on mucosal iron transport and iron retention. The mechanism(s) by which mucosal iron transport is affected during NZGLM supplementation was also investigated. When investigated in vitro, NZGLM and beef both enhanced iron absorption by a similar magnitude compared to egg albumin. The enhancing effect of NZGLM on iron absorption was repeatedly observed using two separate in vitro models; Caco-2 cells and mouse small intestine mounted on Ussing chambers. When investigated in iron-deficient mice, mucosal iron transport and extra-intestinal iron retention were significantly enhanced when an iron supplement was combined with NZGLM compared to egg albumin. Conversely, an inhibitory effect was observed when mice were supplemented with NZGLM for a prolonged period of time prior to consuming an iron supplement. The inhibitory effect of NZGLM was not associated with the dietary iron load. Prolonged NZGLM supplementation inhibits mucosal iron absorption by reducing brush border iron transport. The inhibitory effect of prolonged NZGLM supplementation was observed to be associated with its high calcium content; however other competitive nutrients such as copper, manganese or zinc may also contribute to the inhibitory effect. The main inhibitory effect is proposed to be calcium-stimulated DMT1 internalisation into cytosolic vesicles. This occurs after prolonged or repeated NZGLM supplementation. The findings of this study suggest that NZGLM enhances mucosal iron transport and distribution to extra-intestinal tissues when consumed as a single dose with an iron supplement. For this reason NZGLM may be an alternative iron absorption enhancer to red meat or pork with additional cardio-protective properties. Repeated NZGLM supplementation may reduce mucosal transport; therefore repeated NZGLM supplementation should be moderated in order to ensure that mucosal iron transport is not compromised.